236
B. L. ASTAUROV
In fact, we have just the opposite situation: the 4 n progeny from
crosses of parthenogenetic $ 3 n X
author's earliest experiments (unpublished), several crosses were performed of parthenofemales taken from a 3 n clone, heterozygous for
dominant larval marking Ze(Zebra), with normal 2n males. 601 Fi
caterpillars were obtained showing the segregation 490 Zebra : 111 normal. If 3 n females have the genotypic constitution Zezeze hexaploid
oocytes should have the constitution ZeZezezezeze. In the case of random
paired conjugation and segregation in crosses $ ZeZezezezeze X d zeze )
the theoretical expectation is 480.8 Zebra : 120.2 normal, which presents
a fairly good coincidence with experimental results. There is no doubt,
therefore, that 3 n parthenofemales sometimes become mixoploid and lay
6n eggs (approximately 1% on the average), but no sharp dimensional
difference between 3 n and 6 n oocytes exist.
G. Production of a Self-Reproducing Bisexual Allopolyploid Strain
Unfortunately, autotetraploid B. mori males obtained by the method
described in Section V,F, contrary to their 4 n sisters, are almost sterile.
Just a few autotetraploid males were formerly obtained by centrifugation
of freshly fertilized eggs (Kawaguchi, 1936a). These also proved to be
almost sterile, so that no tetraploid bisexual strain has ever been reared.
An easy way to produce tetraploid females and males as descendants
of mixoploid (3 n -f 6 n) females offered a new opportunity for their
interbreeding, but repeated attempts to breed an autotetraploid strain
invariably failed.
The usual presence of several tetra- or polyvalents in metaphase plates
of first spermatocyte maturation divisions suggests the aneuploidy of
spermatozoa to be the main, or probably the sole, cause of male sterility
(Roginskaya, 1964a,b).
It is well known that a more or less pronounced partial sterility is
a serious obstacle to the experimental creation of autopolyploids in
bisexually reproducing plants; however amphidiploid plants have fairly
good fertility, as was, for instance, demonstrated for the first time in
the classic examples of Raphanobrassica by Karpechenko and of Triticale
by Müntzing.
If the same basic principle is applicable to animals, tetraploid hybrids
between the domesticated B. mori L. (n = 28) and wild silkworm species
B. mandarina Moore (Ussuri and Shanghai races, n — 28) could be
expected to be more or less fertile.
Bombyx mori and B. mandarina have many conspicuous differences
(Astaurov and Ostriakova-Varshaver, 1957a-c). However, despite their
B. L. ASTAUROV
In fact, we have just the opposite situation: the 4 n progeny from
crosses of parthenogenetic $ 3 n X
author's earliest experiments (unpublished), several crosses were performed of parthenofemales taken from a 3 n clone, heterozygous for
dominant larval marking Ze(Zebra), with normal 2n males. 601 Fi
caterpillars were obtained showing the segregation 490 Zebra : 111 normal. If 3 n females have the genotypic constitution Zezeze hexaploid
oocytes should have the constitution ZeZezezezeze. In the case of random
paired conjugation and segregation in crosses $ ZeZezezezeze X d zeze )
the theoretical expectation is 480.8 Zebra : 120.2 normal, which presents
a fairly good coincidence with experimental results. There is no doubt,
therefore, that 3 n parthenofemales sometimes become mixoploid and lay
6n eggs (approximately 1% on the average), but no sharp dimensional
difference between 3 n and 6 n oocytes exist.
G. Production of a Self-Reproducing Bisexual Allopolyploid Strain
Unfortunately, autotetraploid B. mori males obtained by the method
described in Section V,F, contrary to their 4 n sisters, are almost sterile.
Just a few autotetraploid males were formerly obtained by centrifugation
of freshly fertilized eggs (Kawaguchi, 1936a). These also proved to be
almost sterile, so that no tetraploid bisexual strain has ever been reared.
An easy way to produce tetraploid females and males as descendants
of mixoploid (3 n -f 6 n) females offered a new opportunity for their
interbreeding, but repeated attempts to breed an autotetraploid strain
invariably failed.
The usual presence of several tetra- or polyvalents in metaphase plates
of first spermatocyte maturation divisions suggests the aneuploidy of
spermatozoa to be the main, or probably the sole, cause of male sterility
(Roginskaya, 1964a,b).
It is well known that a more or less pronounced partial sterility is
a serious obstacle to the experimental creation of autopolyploids in
bisexually reproducing plants; however amphidiploid plants have fairly
good fertility, as was, for instance, demonstrated for the first time in
the classic examples of Raphanobrassica by Karpechenko and of Triticale
by Müntzing.
If the same basic principle is applicable to animals, tetraploid hybrids
between the domesticated B. mori L. (n = 28) and wild silkworm species
B. mandarina Moore (Ussuri and Shanghai races, n — 28) could be
expected to be more or less fertile.
Bombyx mori and B. mandarina have many conspicuous differences
(Astaurov and Ostriakova-Varshaver, 1957a-c). However, despite their